According to the National Institutes of Health, approximately 28 million Americans have a hearing impairment. Hearing loss covers an age span of approximately 17 in 1,000 children under the age of 18 and approximately 314 in 1,000 adults over the age of 65. This indicates that the incidence of hearing loss increases with age. In addition, ten million Americans have suffered irreversible noise-induced hearing loss, and 30 million more are exposed to dangerous sound levels each day.
One source of these dangerous sound levels is earphones and headphones. Generally, the user of earphones or headphones has no knowledge of or reference for the actual sound level presented to their ears. Without knowledge of the actual audio levels being applied to the ear canal, the user is at risk of accruing hearing damage with long-term use. With the increased use of insert-earphones (also know as in-ear earphones, isolating earphones, or canal-phones) and portable audio players, it is becoming more commonplace and understood that unsafe audio levels are being played and hearing damage is likely to occur. The Occupational Safety and Health Administration (OSHA) and other governmental and industry organizations have published sound-pressure-level versus exposure-time guidelines which indicate safe limits of exposure to noise.
In some instances, an earphone user may understand the risk involved in listening to sound at louder levels, but currently does not have a tool available for determining the level of sound to which he or she is actually being exposed. This problem is further exacerbated by the listening experience that is provided by noise-isolating or insert-earphones. In particular, a user of these earphones no longer has the reference of the ambient environment from which to determine the relative level of reproduced audio. In addition, the audio drivers of insert-earphones provide little of the bone-conduction vibration that bigger headphones or speakers create, which may lead the user into believing that the listening level is lower than actual.
One available method for protecting hearing is a volume limiter that is available on some portable audio devices. However, the protection offered by a Volume limiter is arbitrary because it limits the volume level based solely on the output of the instrument without taking into consideration the sensitivity of the earphones and how efficiently they couple sound to a user's eardrum. Thus, this method may cause the user to over or underestimate the levels of audio to which they are subject, and may provide a false sense of security. In addition, while it is understood that exposure to high sound-pressure-levels can be harmful to one's hearing, the duration of the exposure is key to understanding the relative level of danger. However, the volume limiter solution fails to take into account this duration to the exposure of the sound, which can further offer the user a false sense of protection.